p-glycoprotein

Schisandrol A from Schisandra chinensis reverses P-glycoprotein-mediated multidrug resistance by affecting Pgp-substrate complexes.: Planta Med. 2007 Mar;73(3):212-20 Authors: Fong WF, Wan CK, Zhu GY, Chattopadhyay A, Dey S, Zhao Z, Shen XL

Recent studies have shown that dibenzocyclooctadiene lignans may reverse P-glycoprotein-mediated multidrug resistance (Pgp-MDR) in cancer cells; however, the mechanism of action remains unknown. Through screening of herbs, we found that schisandrol A (SCH) isolated from Fructus Schisandrae (the dried fruit of Schisandra chinensis (Turcz.) Baill.) sensitized Pgp-MDR HepG2-DR cells by interfering with the function of Pgp-substrate complexes. In Pgp-MDR cells, SCH enhanced the cytotoxicity of cancer drugs that are Pgp substrates and restored vinblastine-induced G2/M arrest without lowering Pgp expression. SCH increased cellular retention of Pgp substrates such as rhodamine 123. In Pgp-overexpressing membrane preparations, SCH stimulated basal Pgp-ATPase thus showing some substrate-like function. However, SCH was not a competitive inhibitor for verapamil or progesterone and decreased their Km. In the presence of substrates, SCH decreased the reactivity between Pgp and the monoclonal antibody UIC-2 which is normally increased with active substrate-Pgp complexes. The labeling of active Pgp transport sites by [125I]-iodoarylazidoprazosin was partially blocked by SCH. SCH did not affect the activity of the mutant Pgp F983A suggesting that SCH acted differently than the thioxanthene type of Pgp allosteric inhibitors. Our results suggest that SCH acts by affecting the normal formation and functioning of the Pgp-substrate complexes.

PMID: 17318783 [PubMed - indexed for MEDLINE]

Role of P-glycoprotein in the intestinal absorption of glabridin, an active flavonoid from the root of Glycyrrhiza glabra.: Drug Metab Dispos. 2007 Apr;35(4):539-53 Authors: Cao J, Chen X, Liang J, Yu XQ, Xu AL, Chan E, Wei D, Huang M, Wen JY, Yu XY, Li XT, Sheu FS, Zhou SF

Glabridin is a major constituent of the root of Glycyrrhiza glabra, which is commonly used in the treatment of cardiovascular and central nervous system diseases. This study aimed to investigate the role of P-glycoprotein (PgP/MDR1) in the intestinal absorption of glabridin. The systemic bioavailability of glabridin was approximately 7.5% in rats, but increased when combined with verapamil. In single-pass perfused rat ileum with mesenteric vein cannulation, the permeability coefficient of glabridin based on drug disappearance in luminal perfusates (P(lumen)) was approximately 7-fold higher than that based on drug appearance in the blood (P(blood)). Glabridin was mainly metabolized by glucuronidation, and the metabolic capacity of intestine microsomes was 1/15 to 1/20 of that in liver microsomes. Polarized transport of glabridin was found in Caco-2 and MDCKII monolayers. Addition of verapamil in both apical (AP) and basolateral (BL) sides abolished the polarized transport of glabridin across Caco-2 cells. Incubation of verapamil significantly altered the intracellular accumulation and efflux of glabridin in Caco-2 cells. The transport of glabridin in the BL-AP direction was significantly higher in MDCKII cells overexpressing PgP/MDR1 than in the control cells. Glabridin inhibited PgP-mediated transport of digoxin with an IC(50) value of 2.56 microM, but stimulated PgP/MDR1 ATPase activity with a K(m) of 25.1 microM. The plasma AUC(0-24h) of glabridin in mdr1a(-/-) mice was 3.8-fold higher than that in wild-type mice. These findings indicate that glabridin is a substrate for PgP and that both PgP/MDR1-mediated efflux and first-pass metabolism contribute to the low oral bioavailability of glabridin.

Gomisin A alters substrate interaction and reverses P-glycoprotein-mediated multidrug resistance in HepG2-DR cells.: Biochem Pharmacol. 2006 Aug 2; Wan CK, Zhu GY, Shen XL, Chattopadhyay A, Dey S, Fong WF

Through an extensive herbal drug screening program, we found that gomisin A, a dibenzocyclooctadiene compound isolated from Schisandra chinensis, reversed multidrug resistance (MDR) in Pgp-overexpressing HepG2-DR cells. Gomisin A was relatively non-toxic but without altering Pgp expression, it restored the cytotoxic actions of anticancer drugs such as vinblastine and doxorubicin that are Pgp substrates but may act by different mechanisms. Several lines of evidence suggest that gomisin A alters Pgp-substrate interaction but itself is neither a Pgp substrate nor competitive inhibitor. (1) First unlike Pgp substrates gomisin A inhibited the basal Pgp-associated ATPase (Pgp-ATPase) activity. (2) The cytotoxicity of gomisin A was not affected by Pgp competitive inhibitors such as verapamil. (3) Gomisin A acted as an uncompetitive inhibitor for Pgp-ATPase activity stimulated by the transport substrates verapamil and progesterone. (4) On the inhibition of rhodamine-123 efflux the effects of gomisin A and the competitive inhibitor verapamil were additive, so were the effects of gomisin A and the ATPase inhibitor vanadate. (5) Binding of transport substrates with Pgp would result in a Pgp conformational change favoring UIC-2 antibody reactivity but gomisin A impeded UIC-2 binding. (6) Photocrosslinking of Pgp with its transport substrate [(125)I]iodoarylazidoprazosin was inhibited by gomisin A in a concentration-dependent manner. Taking together our results suggest that gomisin A may bind to Pgp simultaneously with substrates and alters Pgp-substrate interaction.

Voacamine, an alkaloid extracted from Peschiera fuchsiaefolia, inhibits P-glycoprotein action in multidrug-resistant tumor cells.: Int J Oncol. 2005 Dec;27(6):1597-603 Authors: Meschini S, Marra M, Condello M, Calcabrini A, Federici E, Dupuis ML, Cianfriglia M, Arancia G

Multidrug resistance (MDR) in tumor cells is generally associated with increased efflux of the cytotoxic compounds, due to the activation of mechanisms of intracellular transport and to the overexpression of surface proteins, such as P-glycoprotein (Pgp), which act as ATP-dependent molecular pumps. In a previous study, voacamine, a bisindolic alkaloid from Peschiera fuchsiaefolia, was examined for its possible capability of enhancing the cytotoxic effect of doxorubicin (DOX) on resistant human osteosarcoma cells. The effects of voacamine on the cell survival and on accumulation of DOX were investigated on both the parental cell line, U-2 OS-WT, and its resistant counterpart, U-2 OS-R. A differential effect between sensitive and resistant cells on the intracellular DOX concentration and distribution was revealed. In particular, voacamine induced a significant increase of drug retention and intranuclear location in resistant cells. Moreover, the cell survival analysis and the electron microscopic observations revealed an enhancement of the cytotoxic effect of DOX induced by the plant extract. In the present study, a panel of monoclonal antibodies (MAbs), recognizing different and specific structural and functional state of Pgp, was used. By flow cytometry and immunofluorescence confocal microscopy, a dose-dependent increase of the reactivity of Pgp with MAb UIC2, which specifically recognizes an epitope of the drug transporter in its functional conformation, was detected in voacamine-treated U-2 OS-R cells. Conversely, the expression of the epitope recognized by MAb MC57 was downregulated while MAb MM4.17 did not change its binding level to treated and untreated MDR cells. These data suggest that the plant extract reacts with Pgp producing conformational changes with consequent epitope modulation. Taken together, our observations seem to demonstrate that voacamine is a substrate for Pgp and, therefore, interferes with the Pgp-mediated drug export, acting as a competitive antagonist of cytotoxic agents.

MDR- and CYP3A4-mediated drug-herbal interactions.: Life Sci. 2006 Jan 24; Authors: Pal D, Mitra AK

According to recent epidemiological reports, almost 40% of American population use complimentary and alternative medicine (CAM) during their lifetime. Patients detected with HIV or cancer often consume herbal products especially St. John's wort (SJW) for antidepressants in combination with prescription medicines. Such self-administered herbal products along with prescribed medicines raise concerns of therapeutic activity due to possible drug-herbal interactions. P-glycoprotein (P-gp) and cytochrome P450 3A4 (CYP3A4) together constitute a highly efficient barrier for many orally absorbed drugs. Available literature, clinical reports and in vitro studies from our laboratory indicate that many drugs and herbal active constituents are substrates for both P-gp and CYP3A4. Results from clinical studies and case reports indicate that self-administered SJW reduce steady state plasma concentrations of amitriptyline, cyclosporine, digoxin, fexofenadine, amprenavir, indonavir, lopinavir, ritonavir, saquinavir, benzodiazepines, theophyline, irinotecan, midazolan and warfarin. This herbal agent has been also reported to cause bleeding and unwanted pregnancies when concomitantly administered with oral contraceptives. Most of these medicinal agents and SJW are substrates for P-gp and/or CYP3A4. In vitro studies from our laboratory suggest that short-term exposure with pure herbal agents such as hypericin, kaempferol and quercetin or extract of SJW resulted in higher uptake or influx of ritonavir and erythromycin. Hypericin, kaempferol and quercetin also caused a remarkable inhibition of cortisol metabolism with the percent intact cortisol values of 64.58%, 89.6% and 90.1%, respectively, during short-term in vitro experiments. Conversely, long-term exposure of herbal agents (hyperforin, kaempferol and quercetin) showed enhanced expression of CYP3A4 mRNA in Caco-2 cells. In another study, we observed that long-term exposure of hypericin, kaempferol, quercetin and silibinin resulted in higher MDR-1 mRNA expression in Caco-2 cells. Therefore, herbs can pharmacokinetically act as inhibitors or inducers. Medicinal agents that are substrates P-gp-mediated efflux and/or CYP-mediated metabolism are likely to be potential candidates for drug-herbal interactions. The duration of exposure of cells/healthy volunteers/animals to herbals appears to be critical for drug-herbal interaction. An increase in plasma drug concentration is possible during concomitant administration of SJW and prescribed drugs. In contrast, prolonged intake of herbal supplement followed by drug administration may result in subtherapeutic concentrations. Therefore, clinical implications of such drug herbal interactions depend on a variety of factors such as dose, frequency and timing of herbal intake, dosing regimen, route of drug administration and therapeutic range. In vitro screening techniques will play a major role in identifying possible herb-drug interactions and thus create a platform for clinical studies to emerge. Mechanisms of drug-herbal interaction have been discussed in this review article.

Inhibitory effect of thai plant extracts on P-glycoprotein mediated efflux.: Phytother Res. 2006 Jan 5;20(1):79-81 Authors: Junyaprasert VB, Soonthornchareonnon N, Thongpraditchote S, Murakami T, Takano M

Curcuminoids from Curcuma longa L. and extracts of Psidium guajava L., Andrographis paniculata (Burm. f.) Nees, Phyllanthus emblica L. and Solanum trilobatum L. were investigated for their inhibitory effect on P-glycoprotein (P-gp) on the efflux transport of rhodamine 123 (Rho-123 ) in Caco-2 cells and rat ileum. Of the five tested samples, curcuminoids and an extract of P. guajava showed the highest inhibitory effect on P-gp mediated efflux of Rho-123 in Caco-2 cells. Additionally, they were found to have equal potential in inhibiting Rho-123 efflux transport from serosal to mucosal surfaces of the rat ileum. Copyright (c) 2006 John Wiley & Sons, Ltd.

Inhibitory effect of thai plant extracts on P-glycoprotein mediated efflux.: Phytother Res. 2006 Jan 5;20(1):79-81 Authors: Junyaprasert VB, Soonthornchareonnon N, Thongpraditchote S, Murakami T, Takano M

Curcuminoids from Curcuma longa L. and extracts of Psidium guajava L., Andrographis paniculata (Burm. f.) Nees, Phyllanthus emblica L. and Solanum trilobatum L. were investigated for their inhibitory effect on P-glycoprotein (P-gp) on the efflux transport of rhodamine 123 (Rho-123 ) in Caco-2 cells and rat ileum. Of the five tested samples, curcuminoids and an extract of P. guajava showed the highest inhibitory effect on P-gp mediated efflux of Rho-123 in Caco-2 cells. Additionally, they were found to have equal potential in inhibiting Rho-123 efflux transport from serosal to mucosal surfaces of the rat ileum. Copyright (c) 2006 John Wiley & Sons, Ltd.

Inhibition of P-glycoprotein-mediated transport by extracts of and monoterpenoids contained in Zanthoxyli fructus.: Toxicol Appl Pharmacol. 2005 Dec 1;209(2):167-73 Authors: Yoshida N, Takagi A, Kitazawa H, Kawakami J, Adachi I

Citrus (rutaceous) herbs are often used in traditional medicine and Japanese cuisine and can be taken concomitantly with conventional medicine. In this study, the effect of various citrus-herb extracts on P-glycoprotein (P-gp)-mediated transport was examined in vitro to investigate a possible interaction with P-gp substrates. Component monoterpenoids of the essential oil in Zanthoxyli fructus was screened to find novel P-gp inhibitors. LLC-GA5-COL150 cells transfected with human MDR1 cDNA encoding P-gp were used. Cellular accumulation of [3H]digoxin was measured in the presence or absence of P-gp inhibitors or test samples. Aurantii fructus, Evodiae fructus, Aurantii fructus immaturus, Aurantii nobilis pericarpium, Phellodendri cortex, and Zanthoxyli fructus were extracted with hot water (decocted) and then fractionated with ethyl acetate. The cell to medium ratio of [3H]digoxin accumulation increased significantly in the presence of the decoction of Evodiae fructus, Aurantii nobilis pericarpium, and Zanthoxyli fructus, and the ethyl acetate fraction of all citrus herbs used. The ethyl acetate fraction of Zanthoxyli fructus exhibited the strongest inhibition of P-gp among tested samples with an IC50 value of 166 microg/mL. Then its component monoterpenoids, geraniol, geranyl acetate, (R)-(+)-limonene, (R)-(+)-linalool, citronellal, (R)-(+)-citronellal, DL-citronellol, (S)-(-)-beta-citronellol, and cineole, were screened. (R)-(+)-citronellal and (S)-(-)-beta-citronellol inhibited P-gp with IC50 values of 167 microM and 504 microM, respectively. These findings suggest that Zanthoxyli fructus may interact with P-gp substrates and that some monoterpenoids with the relatively lower molecular weight of about 150 such as (R)-(+)-citronellal can be potent inhibitors of P-gp.